ATBS is in use in wide fields, for example, as a modifier for acrylic fiber, a monomer raw material for dispersing agent or coagulating agent, a monomer raw material for thickening agent of cosmetic, or a monomer raw material for production of a chemical used in higher-order recovery of crude oil.
A polymer produced from the ATBS (raw material monomer) used in the above applications is required to have, in particular, a high molecular weight. Therefore, the ATBS used in the above applications need to be minimized in the content of substances hindering the polymerization and have stable quality.
ATBS is ordinarily produced by subjecting acrylonitrile, sulfuric acid and isobutylene to an addition reaction. ATBS is a white, needle-like crystal at a normal state and has a melting point of 185° C. (for example, Patent Literature 1).
In the above addition reaction, the tree components of acrylonitrile, sulfuric acid and isobutylene react at an equimolar ratio stoichiometrically. However, acrylonitrile is used ordinarily in a large excess relative to sulfuric acid and isobutylene, because acrylonitrile functions also as a reaction medium.
ATBS is insoluble in acrylonitrile. Therefore, the reaction product obtained by the reaction is in a slurry state in which ATBS separates out in acrylonitrile. In production of ATBS, it is ordinarily conducted to separate a crude ATBS from the slurry and then purify the crude ATBS in the next purification step.
The purification method includes a method of washing the crude ATBS with acrylonitrile (for example, Patent Literature 1).
There are also a method of recrystallizing the crude ATBS from methanol (for example, Patent Literature 2) and a method of purifying the crude ATBS using an anion exchange resin (for example, Patent Literature 3). Further, there is known, for example, a method of subjecting an aqueous solution of ATBS to distillation in the presence of acrylonitrile to remove water and obtain an acrylonitrile dispersion of ATBS and then separating ATBS from the dispersion by filtration (for example, Patent Literature 4).
However, the substances hindering the polymerization in ATBS have not been identified exactly. Therefore, the above needs have been satisfied by purifying ATBS sufficiently. This method of sufficient purification is not a special method for removing particular substances hindering the polymerization of ATBS, because such substances are not yet identified. There has been used simply a method ordinarily used for enhancement of purity. Therefore, there occurs, in some cases, excessive purification. As a result, the concentration of impurities in the ATBS obtained is unstable and varies each time.    Patent Literature 1: JP-B-1975-30059 (Example 1)    Patent Literature 2: JP-A-2004-359591 (Claim 1)    Patent Literature 3: JP-A-2004-143078 (Claim 1)    Patent Literature 4: JP-A-2004-277363 (Claim 1)